sched/cpuacct: Check for NULL when using task_pt_regs()

task_pt_regs() can return NULL for kernel threads, so add a check.
This fixes an oops at boot on ppc64.

Reported-and-Tested-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Tested-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: Anton Blanchard <anton@samba.org>
Acked-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: efault@gmx.de
Cc: htejun@gmail.com
Cc: linuxppc-dev@lists.ozlabs.org
Cc: tj@kernel.org
Cc: yangds.fnst@cn.fujitsu.com
Link: http://lkml.kernel.org/r/20160406215950.04bc3f0b@kryten
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c
index df947e07aac1d7d668e3a4d6a0feee9f7a35cc73..41f85c4d09387a8bd03299ef00f6e79482f68b40 100644 (file)
--- a/kernel/sched/cpuacct.c
+++ b/kernel/sched/cpuacct.c
@@ -316,12 +316,11 @@ static struct cftype files[] = {
 void cpuacct_charge(struct task_struct *tsk, u64 cputime)
 {
        struct cpuacct *ca;
-       int index;
+       int index = CPUACCT_USAGE_SYSTEM;
+       struct pt_regs *regs = task_pt_regs(tsk);
 
-       if (user_mode(task_pt_regs(tsk)))
+       if (regs && user_mode(regs))
                index = CPUACCT_USAGE_USER;
-       else
-               index = CPUACCT_USAGE_SYSTEM;
 
        rcu_read_lock();